This paper presents a new copyright protection technique using colour watermarks. The watermark is a RGB colour image where each pixel is represented by 24 bits. The RGB colour watermark is first preprocessed by converting it into binary sequence. The preprocessed colour watermark (binary image) is embedded multi-times into the green channel of the RGB host image by modifying the very low frequency coefficients of the DCT transformation. The new technique can resist classical attacks such as JPEG compression, low pass filtering, median filtering, cropping, and scaling attacks. Moreover, the recovery method is blind since it does not need the original host image for extraction. The proposed method implemented using a graphical user interface (GUI) to open, select, attack, evaluate and display the results of both the host image and colour watermark image. The implemented GUI is much easier for the end users to learn more than the traditional algorithms that need commands to be know and memorized. © 2011 IEEE.